We have dissociated myocardial muscle cells from adult rats and rabbits. These preparation are being used to study the contractile, electrophysiological, and biochemical characteristics in a variety of different conditions. In particular we have been able to identify in these isolated cells a longitudinally propagating wave which occurs spontaneously when the cell is not being electrically stimulated and is considered at rest and has a normal resting membrane potential. These "waves" are likely to represent the phenomenon of calcium induced calcium release (CICR) and are the cause of the scattered light intensity fluctuations (SLIF) which our laboratory has studied in the past in multicellular preparations. With our work we have attempted to validate single cells as a model for the study of mechanisms of excitation-contraction coupling and in particular of CICR.